Exam 2 Flashcards
Chapters 4 & 9
Overview of the visual Pathway
Object has light energy > eye > lateral geniculate nucleus (LGN) in the thalamus > Visual receiving area of cortex
Optic Nerve
Comprised of ganglion cells
Optic Chiasm
Neural cross-over pt
-Ipsilateral - Retinal fibers remain on same side of brain (sends to 2, 3, 5 on LGN)
-Contralateral - Retinal fibers cross to other side of brain (sends to 1, 4, 6 on LGN)
-Found with help from “man whose wife is a hat”
LGN (lateral geniculate nucleus)
Part of thalamus, first syn of optic nerve
-90% of optic nerve fibers arrive here (other 10% of superior colliculus)
-Also recieve from brainstem, thalamus neurons, and the cortex
What are the three visual cortexes
Primary visual cortex (PVC)
Secondary Visual Cortex (SVC)
Extrastriate Cortex
LGN recieves more input from _ than the retina
More input from the cortex
The smallest signal of all is from _ to _
The LGN to the cortex
-Sending 4 nerve impulses to the cortex out of 10 coming from retina
Primary Visual Cortex (PVC)
In occipital lobe, AKA striate or striped cortex
Secondary Visual Cortex (SVC)
Areas immediately surrounding PVC
Extrastriate Cortex
2 pathways:
-Dorsal pathway - Parietal lobe
-Ventral pathway - Temporal lobe
Types of ganglion cells
P (parval) cells
M (magno) cells
W cells
P (parval) cell
Sm cell body w/ dense but short branching, representing 80% of retinal ganglian cells
M (magno) cells
Lg cell body w/ sparse but long branching, representing 20% of retinal ganglion cells
Phys aspects of P-cells
P cells have a slower production rate, sustained response, and small RF (fovea & periphery) w/ L contrast sensitivity
-Responds to H illumination & is color sensitive
Phys Aspects of M-cells
Rapid conduction rate, transient response, large RF (Periphery) w/ H contrast sensitivity
-Responds to L illumination & no color
Bhvrl consequences of P
-Detailed form analysis
-Detecting fine detail (ex, texture and pattern)
-Shape and depth
-Color vision
Bhvrl consequences of M-cells
-Motion detection
-REM
-Temporal analysis
-Some depth perception
Superior Colliculus
Detects stim presence, not nature
-Where 10% of ganglion cells from retina go
-Multisensory cells - visual, auditory, and some tactile
-“Secondary visual pathway”
The LGN
In the thalamus, receives 90% of retina cells, regulating info flow to retina to visual cortex
-Firing rate is sensitive to arousal
-Has retinotopic mapping
-“Post office of senses”
Retinotopic mapping
Location on LGN corr w/ retina location, neighbor on LGN = neighbor on retina
LGN’s 6 Layers
Layers 1 & 2 - Magnocellular layers
3, 4, 5, & 6 - P-cell
-Ipsilateral sends to 2, 3, 5
-Contralateral sends to 1, 4, 6 (best & worse on one team)
Impulse from LGN to Striate Cortex: How many, and details
1.5M axons from each LGN transmit info to striate cortex (PVC)
-Info from LGN is “crude”
-Represents small light changes to complex patterns
-Each fracture of visual cortex is rep w/in an individual/group of neurons
Hubel & Wiesel (1982) Cat Study
Cat experiment showing slides discover cortical neurons didn’t fire to small spot of light, distinguishing 3 neurons: simple, complex, and end-stopped cells
Simple Cell
Have RF w/ inhibitory & excitatory regions
-Not arranged by center surround
-Detect lines & edges of specific orientation
Complex Cell
Responds to line orientation & particular direction of mvmt
End-Stop (Hypercomplex) Cell
Represents M complex structure, having complex response to specific length, width, & particular direction
Cortex Cells are often called _ b/c _
Often called feature cells b/c if its not their feature/job, they won’t fire/ do it!
Organization of Striate Cortex Found Via
Oblique probe penetration
Perpendicular penetration
oblique probe penetration
Revealed retinotopic mapping (similar to LGN) w/ systematic displacement, AKA cortical magnification
-Fovea allocates 3-6X more cortical tissue vs periphery (8-10% of cortex)
G cells in fovea vs periphery
Fovea - 50,000 g-cell sq/mm
Periphery - 1,000 g-cells sq/mm
Perpendicular Penetration
Neurons had RF at same location on retina
Orientation Columns
Neurons fire MAX to lines of same orientation
-Adjacent columns have sim but diff orientations
-1mm across cortex, cells respond to entire 180 degree orientation
Ocular Dominance Column
Neurons organized to the eye that they respond best to
-Ocular dom - Prefer to use 1 eye over the other
-Column alt in a L > R pattern every .25 to .50 mm across the cortex
Hypercolumns
1mm block of cortex sserving as processing model - having :
Location on retina (1mm)
Orientation on retina (1mm)
Dominance presentation L to R eye (1mm)
Selective adaptation
Neurons tuned to specific stim fatigue when exposure is long
-Fatigue = adaptation stim, DEC firing rate. Repeated presentation of stim = less firing
*First VS 4th bite of great sammich
-Selective = Only respond to specific stim adaptation
*“Like life, further in = need more complexities”
Grating stim & Contrast Threshold
Alt black and white bars
Threshold = Diff in intensity which bars can be barely seen
-Adapting vertical = INC in contrast threshold
Lesioning (ablation) experiments
1) train animal on task
2) Destroy part of brain
3) Retrain animal on task, see what it can no longer do
4) Results show parts of brain that do specific bhvr
Object Discrimination & Monkey Brains
Monkey is shown an object, then presented with two choice tasks (target or another object), then rewarded for detecting the target object.
-Area removed is temporal lobe = object discrimination suffers (ventral pathway)
Landmark Discrimination problem
Monkey is trained to pick the food well next to a cylinder
-Area removed is parietal lobe = landmark discrimination task suffer (dorsal pathway)
M & P Layers
Magnocellular - Mvmt
-M-Ganglion > Magno LGN > V1 > dorsal > parietal lobe
Parvocellular - Color, texture, depth
-P-ganglion cell > Parvo LGN > V1 > ventral > temporal lobe
Where or HOW?
Where pathway may be “how”:
-Dorsal stream shows function of location & action
-Locating object & directing action toward it
-Neuropsych evidence - Patient DF (what/ventral damaged) w/ bad static orientation matching
Possible dissociation
Size Illusion Task
Length Estimation - Exp illusion (ventral)
Grasping Task - No diff
Illusion supports perc and action done via diff mechanisms
Brain bits & functions
Modules - Faces, places, mvmt, ect
Maps - Magnifciation
Columns - Location, orientation, ocular dom
Streams - What, where, how
Sensory & Distributed Coding
Objects seen via neural firing, “grandmother cell” - specificity coding
Distributed coding - Pattern of firing across many neurons
Types of Distributed coding
Population Coding & Sparse coding
Population Coding
Objects represented by pattern of firing from large groups of neurons
-Covers lg amount of patterns/stim
Sparse Coding
Objects rep by pattern of firing from small group of neurons (rest are silent)
-Good evidence in vision, hearing, and smell
Cue Approach (size & depth perc, types)
Using depth cues, learned via exp, once learned auto access
-Oculomotor cues - Accommodation
-Pictorial (monocular cues) - Most sources about depth are monocular cone eye needed
*Used by artists, static cues
Types of monocular cues
-Occlusion
-Size
-Texture gradient
-Linear perspective
-Atmospheric Perspective
-Heigh, elevation (horizon)
Occlusion Monocular Cues
Interposition, overlap partly covered objects appear further away
-Primary source of depth info
Size monocular cues (2 objects)
If 2 same size objects are viewed together, the one that occupies more retinal space is closer
-Familiarity to size, top down using prior knowledge
Texture gradient monocular cues
Texture becomes denser as distance INC
Linear Perspective Monocular Cues
Parallel lines appear to meet/converge in distance
(females have closer near point)
Atmospheric Perspective Monocular Cues
Arial perspective
Distance objects look blurry and bluish
Height/elevation cues (horizon)
Objects near horizon appear further away
Movement-produced cues
Motion parallax
Deletion & accretion
Motion parallax mvmt produced cues
When you move your head sideways, objects at diff distances appear to move at diff speeds
-Far objects move slowly; near by objects rapidly
Deletion & Accretion
-2 objects staggered at different distance
-Farther objects will be deleted (covered) when move in one direction
-Or be accreted uncovered when move in the opposite direction
Binocular Cues
2 eyes separated by ~6cm, each having diff image
-Corresponding point on retina connects to same place on cortex
Horopter
Imaginary circle passing through point of focus
-Not on = non-corre. point = disparate images
-Angle of disparity - angle btwn horopter & non-corre. point (Lg = close)
Angle of disparity
Angle btwn horopter and disparate image/non-corre. point
-Lg angle = closer to object
-In front = crossed (eyes) disparity, beyond = uncross disparity
Phys Support Monkey Brain Study
Allowed us to see recordings of neurons in parietal lobe, revealing some cells respond to pictural cues while others to binocular disparity
Binocular disparity
Depth/disparity selective cell best responds to specific degree of disparity images on R&L retinas
-Best 1/2 (0.5degree)
Monocular kitten rearing study
Keeping one eye shut for 6 months found to have caused bad depth perception b/c DEC in binocular neurons
Microstim binocular rearing study
Stim brain w/ electricity impacts depth perception when wrong neurons are stim
Dev Phys of binocular neurons
Study looking at cat’s striate cortex found is 80% binocular neurons that must dev during critical sensitive period (before 6m)
-Too old = crit pd passes & neurons don’t dev properly
Holway & Boring’s Size Perc Study
Looking at projected circle down a hallway, concluded:
-W/ depth cues = accurate (lg w/ distaance)
-1 Eye closed = accurate but thought to be larger when distance is INC
-Looking thru peephole, judged on vis angle & actual size = inaccurate
-No depth perc cues, judge w/ vis angle
How can the moon pass over the sun?
Despite the moon being smaller than the sun, to us it can block the sun b/c it is closer (2000 vs 80000 miles)
Size Constancy
Size = same even when size on retina changes
Veridical perc
Perc matches actual phys action
Size Distance Scaling Equation
S = K ( R x D)
S - Size perc
K = Consonant
R = Retina size
D = Perc distance
Emmert’s Law
S = R x D
Misapplied size constancy scaling
Constancy scaling is for 3D, misapplied looking at 2D
<—–>
>—–< Bottom perc bigger b/c uncon perc arrows as inside or outside
Outside = Seems close
<—–>
Inside = Seems far
>—–<
Conflicting Cues Theory
Perc of line length depends on actual length of vertical lines & overall length of figure, compromise = conflicting cue
